System of digital measurement of the position of a first member slidably mounted upon a second rotating member

ABSTRACT

A system of digital measurement of the position of a first member slidably mounted upon a second rotating member comprises a first stationary coupling coil and a second similar coupling coil mounted upon the second member coaxially with the rotary axis thereof and parallel to said first coil. Energy produced by a stationary high frequency power generator is fed to said first coil and transmitted inductively to the second coil from which it is derived and rectified, to provide d.c. power upon the rotating member for the energization of a pulse former producing digital position signals proportional to the movement of said first member and of a high-frequency signal generator modulated by said position signals. The output energy of the signal generator is transmitted inductively via said coils in a direction opposite to the transmitting direction of the power energy and the signal energy derived from the first coupling coil demodulated, to retrieve the original position signals for application to a translating device. In order to effect full decoupling between the power and signalling circuits, the power energy is transmitted in symmetrically balanced relation and the signal energy is transmitted in unbalanced relation to the center points of the coils as potential reference.

United States Patent Glantschnig et al. I

[54] SYSTEM OF DIGITAL MEASUREMENT OF THE POSITION OF A FIRST 7 MEMBERSLIDABLY MOUNTED UPON A SECOND ROTATING MEMBER [15] 3,657,717 [451 Apr.18,1972

3,098,187 7/1963 Sciaky ..3l8/640X Primary Examiner-Thomas A. RobinsonAttorney-Greene & Durr [72] lnventors: Fritz Glantschnig, Neuenhof;Manfred ABSTRACT Nussbaumen both of Swmerland A system of digitalmeasurement of the position of a first [73] Assignee: PatelholdPatentverwertungs- & Elektrof" shdably "P seqond rotating p Holding HSwitzerland comprises a first stationary coupling coil and a secondsimilar coupling COli mounted upon the second member coaxially [22]Flled: June 5, 1970 with the rotary axis thereof and parallel to saidfirst coil. Ener- 21 I, N 4 8 4 gy produced by a stationary highfrequency power generator is I 1 App 0 4 fed to said first coil andtransmitted inductively to the second coil from which it is derived andrectified, to provide d.c. [30] Forelgn Application Priority Data powerupon the rotating member for the energization of a pulse formerproducing digital position signals proportional to June 6, 1969Switzerland ..8636/69 the movement of said first member and of a g q y[52] U s 340/347 SY 340/347 P 340/195 signal generator modulated by saidposition signals. The out- [51] cosc 9/o4 H631 13/00 put energy of thesignal generator is transmitted inductively [58] Fieid /347 PR 3 196 345via said coils in a direction opposite to the transmitting 340/177 R /65 720 4 4 5 direction of the power energy and the signal energy derived,

R 5 3 6 640 from the first coupling coil demodulated, to retrieve theoriginal position signals for application to a translating device. [56]References Cited In order to effect full decoupling between the powerand signalling circuits, the power energy is transmitted in symmet-UNITED STATES PATENTS rically balanced relation and the signal energy istransmitted in unbalanced relation to the center points of the COliS aspoten- 3,268,880 8/1966 Miller ..340/ 195 X tial reference 3,530,4499/1970 Andersen..... ....340/l95 X 3,172,107 3/ 1965 Morris ..343/6 .5 X9 Claims, 3 Drawing Figures a 1 r0 Pas/now $0M! l mail :3? i

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2 Sheets-Sheet 1 h4g1. IEATH ATTORNEY Patented April 18, 1972 PatentedApril 18, 1972 3,657,717

2 Sheets-Sheet 3 ATTORNEY SYSTEM OF DIGITAL MEASUREMENT OF THE POSITIONOF A FIRST MEMBER SLIDABLY MOUNTED UPON A SECOND ROTATING MEMBER Thepresent invention relates to the continuous digital measurement of theposition of a first member slidably mounted upon a second rotatingmember, in particular to the measurement of the movement of the planarslide mounted upon the planar disk of a machine tool, while the toolengages the work during rotation of said disk and the movement of theslide is measured directly upon said disk and converted into electricsignals by means of an analog-digital converter.

In many types of machine tools, in particular tools for the carrying outof boring and milling operations by way of a radial slide mounted upon arotating disk, the problem exists to continuously measure the exactposition of the tool or slide while the disk rotates and the toolengages the work.

' The problem assumes a special importance where a high accuracy isrequired of the diameter operated on and where the movement of the slideis to be controlled numerically, such as in the case of automatic toolcontrol.

It is already known, in order to translate the position of the slide, toprovide an analog-digital converter in the gear train of the slideexteriorly of the latter, with the number of digital pulses beingsuitably chosen in relation to the transmission ratio such as to producefor instance one pulse for each onethousandth inch displacement of theslide.

Among the various disadvantages of a solution of this type are lowaccuracy and lack of reproduceability, due mainly to the fact that thedrive of the slide may comprise as many as 20 gear pairs resulting in atotal play, even in case of extreme precision construction, being l to30 times the practically required value or accuracy. Furthermore, such agreat play of the parts makes it difficult to approach a desiredposition from different directions, whereby to practically limitoperation and measurement to a single direction of movement. Additionalinaccuracy may be introduced by torsion effects within the gear traindepending upon the load and undeterminable in advance. Finally, themeasuring accuracyis subject to deterioration caused by wear and age ofthe gears.

In order to overcome the afore-described difficulties, it is principallypossible to measure the movement of the slide directly upon the disk bymeans of a converting device comprising a rack and pinion in conjunctionwith an analog-digital converter translating the rotational angle of thepinion into electric digital signals derived from the disk via slip ringconnectors. This solution involves however other difficulties byrequiring at least four separate slip rings and sliding brushes, thatis, two for the power transmission and two for the signal transmissionto and from the rotating disk, a requirement difficult to fulfillconstructionally and satisfactorily in practice. Besides, it isnecessary to absolutely avoid even relatively short interruptions of therelatively moving contacts, to ensure a safe and distortion-freetransmission of the measuring signals or pulses. In order to minimizethis drawback, multiple ring and brush devices would have to be used,whereby tofurther complicate both the construction and operation of asystem of this type.

In view of the difficulties mentioned and of the normally prevalingconsiderable smudging and soiling of the parts by metal chips and dust,and furthermore in view of the impact and vibratory forces to which theparts are subjected during operation, a practically satisfactorysolution of the problem herein described and involved could not berealized in the past.

Accordingly, an important object of the present invention is theprovision of a new improved system of the referred to type for thecontinuous digital measurement of the movement or position of a slidablemember mounted upon a rotating member, which new system is substantiallydevoid of the afore-mentioned and related difficulties and drawbacks,which is practically realizable by the use of conventional constructionelements and circuitry, and which will enable the achievement ofextremely high measuring accuracies in conjunction with high operatingsafety and reliability.

The invention, both as to the foregoing and ancillary objects as well asnovel aspects thereof, will be better understood from the followingdetailed description of a preferred practical embodiment, taken inconjunction with the accompanying drawings forming part of thisdisclosure and in which:

FIG. 1 is a schematic diagram of a digital position measuring system fora slidable member mounted upon a rotating member, constructed inaccordance with the principles of the invention;

FIG. 2 more clearly shows the mechanical arrangement of the rotating andslidable members; and

FIG. 3 shows schematically and in perspective view a preferreddigital-analog converter for use in conjunction with the invention.

Like reference characters denote views of the drawing.

With the foregoing objects in view, the present invention involvesgenerally the provision of means in a system of the referred to type forthe inductive transmission of highfrequency power energy from astationary member to the rotating member of the system and rectificationof said energy to provide dc. power upon said rotating member for theenergization of an analog-digital converter transforming the move-' mentor position of the slidable member into proportionate digital signals,on the one hand, and for the energization of a high-frequency signalgenerator disposed upon said rotating member and preferablyfrequency-modulated by said digital signals, on the other hand. Themodulated high-frequency energy is re-transmitted inductively to saidstationary member for demodulation and utilization of the resultantoriginal posilike parts in the different tion signals to energize atranslating device, such as a counter for indication or for comparisonof the signals with position control or command signals in a feed backtype automatic control system.

Transmission of both the high-frequency power and signalling energies toand from the rotating member is effected by way of a pair of inductivecoupling coils mounted respectively upon the stationary member and therotating member and designed and relatively arranged or aligned in sucha manner as to maintain a substantially constant coupling coefficientindependently of the relative rotation of the members. For this purpose,the use of a pair of two-tum flat coils arranged parallel to one anotherand concentrically with the rotary axis has been found to ensuresatisfactory and optimal results in practice. In order to suppressmutual interference between the power and signal frequency circuits, thepower and signal generators operate with different carrier frequenciesand/or the respective energies are transmitted via said coils insymmetrically balanced and unbalanced relation, respectively, to thecenters of the coil windings as potential reference points. 7

In order to discriminate between difierent directions of movement, apair of digital pulse series are produced in relative quadrature phaserelation with one of the series leading or lagging respectively theother series in dependence upon the direction of movement of the slideor like movable member. Both pulse series are combined into a singleternary series of both positive and negative pulses, with the positivepulses representing one direction and the negative pulses representingthe opposite direction of movement, said ternary pulses beingtransmitted by modulation of the signal generator and converted into theoriginal quadrature pulses for application to the translating or controldevice, these and other details and novel features as well as advantagesof the invention becoming more apparent as the description proceeds inreference to the drawing.

Referring at first to FIG. 2, SM denotes a stationary part or member ofa machine tool or the like and RM denotes the rotating member havingmounted thereon a movable member or slide 28. Items 10 and 11 are a pairof flat inductive coupling coils disposed parallel to one another andmounted respectively in grooves 26 and 27 of the members SM and RMconcentrically with the rotary axis x-x of the member RM. The grooves 26and 27 are filled with a synthetic resin or the like insulating andsealing material. As furthermore shown in FIG. 1, each of thecoils l and11 consists preferably of two concentric turns disposed in radial planesin respect to the rotary axis .x-x with one pair of adjoining ends ofeach pair of turns connected to provide center or reference points C,and C respectively, for the purpose as further described hereinafter. Asa consequence, the coupling coefficient between the coils remainssubstantially constant during relative rotation of the members. Thedistance between the coils 26 and 27 being non-critical may berelatively large, as may be the air gap 25 about 2 mm in practicebetween the members SM and RM. Accumulation of metal dust and otherforeign matter in the gap 25 has substantially no effect on theinductive transmission of high-frequency energy between th coils.

Referring more particularly to FIG. 1, wherein the stationary parts uponmember SM are shown to the right and the rotating parts on the member RMare shown to the left of of the dividing line y-y, the numeral 12denotes an HP (highfrequency) power generator whose output E isamplified by the HF power amplifier 13, to produce a final output E ofabout watt applied to the terminals A and A of the coupling coil 10 inpush-pull fashion in respect to the center or reference point C,. Due toeddy current losses in the metal masses and to the relatively loosecoupling between the coils 10 and 11, the efficiency of transmission isabout that is, the power induced in the coil 11 equals about 1.5 watt inthe referred to example. This has been found sufficient for theenergization of the integrated circuits and other devices disposed uponthe member RM and described in the followmg.

The HF current induced in the coil 11 is applied, via terminals B and Bof the coil to a conventional rectifier power supply 14 in which the HFenergy is converted into d.c. energy. In the example shown, the dc.power thus provided is in the form of a first +5 V supply voltage Ebeing preferably stabilized by a Zener diode to produce a constantoutput current of 50mA, and a second balanced -12V and +12V supplyvoltage E, for the energization of an HF signal generator 15, poweramplifier and other circuits and parts disposed upon member RM.

The signal generator 15 is modulated, preferably by frequency modulationby the aid of a capacitive diode, by the digital signals e produced bythe position signal generator 16, limiter l7 and directional encoder 18,to result in a modulated HF signal e, amplified by the amplifier 20. Theamplified HF signal e, is applied, via the center point C to the coil 11for transmission to a receiving circuit upon thejmember SM including anHF filter 21, HF amplifier 22 anda frequency discriminator 23. Thediscriminator 23 serves in a known manner to convert amplified HFreceiving signal e into the final signal e, which corresponds to theoriginal position equal e applied to generator 15. I

More particularly and as more clearly described hereinafter, theposition signal generator 16 is designed to produce a pair of sinusoidaloutput signals e, and e withthe signal e leading or lagging respectivelythe signal e, by 90 in dependence upon the directional movement of theslide or member 28 relative to the member RM, FIG. 2. The signals e, ande are converted into square pulses e, and e in the pulse shaper and thequadrature square pulses combined in the directional encoder 18 into asingle ternary modulating signal e applied to the generator 15 andhaving positive and negative pulses corresponding respectively todifferent directions of movement of the member 28. The encoder 18 maycomprise means to differentiate the signals e, and e and to logicallycombine'the differentiated signals, to result in the modulating signal eIn order to prevent mutual interference between the power and signalfrequency circuits, the HF generator 12 may have a carrier frequencydiffering from the carrier frequency of the generator 15. In a practicalexample, the power frequency may be 150 kilocycles and the signalfrequency 250 kilocycles, as indicated in the drawing. Alternatively oradditionally,

- thepower and signal energies passing in different directions betweenthe coils l0 and 11 may be transmitted in symmetrically balanced andunbalanced relation respectively to the center or reference points C,and C, as shown, to effect full decoupling between the power and signalfrequency circuits.

. FIG. 3 shows a preferred photo-electric analog-digital converter forproducing position signals representative of the movement of member 28.For this purpose, the latter carries a rack 30, FIG. 2, engaged by apinion 31 to the shaft 32 of which is connected the analog-digitalconverter 16 translating the rotational angle of the pinion intoproportionate numbers of digital pulses. More particularly, shaft 32carries a rotating shutter disk having alternate peripheral opaque andtransparent segments aligned with a segmental shutter 36 stationaryrelative to the disk 35 and having two rows of similar shutter segmentsaligned with the segments of disk 35. The two rowsof stationary segmentsare relatively displaced to result in a pair of quadrature signals e,and e, respectively in the output circuits of two sets of photocells 37and 40 coordinated and aligned with the shutter 36. The photocells 37are illuminated, via the shutters 35 and 36 by a light source 33 andlens 34. The light source is advantageously in the form of a galliumarsenic diode in view of the relatively small operating power required.The converter 16 together with the remaining parts and integratedcircuit upon member RM may be constructed as a unit in the form of amodule for removable mounting upon said member. As is understood, anyequivalent analog-digital converter may be used for the purpose of theinvention.

In the foregoing, the invention has been described in reference to anexemplary device or embodiment. It will be evident however, thatvariations and modifications, as well as the substitution of equivalentparts or circuits for those shown herein for illustration, may be madein accordance with the broader scope and spirit of the invention.

We claim:

'1. A system of digital measurement of the position of a first memberslidably mounted upon a second rotating member comprising incombination:

1. a first stationary coupling coil,

' 2. a second similar coupling coil upon said rotating member coaxialwith the rotary axis thereof and parallel to said first coil, v

3. a stationary high-frequency power generator connected 4. meansmounted on said second memberand including rectifying means connected tosaid second coil, to rectify the energy induced in said second coil fromsaid first coil and provide a dc. power source upon said second member,

5. means mounted on said second member and energized by said powersource to produce digital signals representative of the position of saidfirst member relative to said second member,

6. a high-frequency signal generator mounted upon said i, second member,

7. means to modulate the output signal of said signal generator by saiddigital signals, 1

8. means to apply the output energy of said signal generator 1 to saidsecond coil,

9. a stationary receiving means connected to said first coil to derivesignal energy induced in said first coil from said second coil, and

10. demodulating means connected to said receiving means,

to reproduce the original digital signals.

2. A measuring system as claimed in claim 1, wherein the carrierfrequency of said signal generator is different from the carrierfrequency of said power generator.

3,-A measuringsystem as claimed in claim 1, wherein said coils areprovided with center taps and the energy of said power generator istransmitted in symmetrically balanced relation and the energy of saidsignal generator is transmitted in unbalanced relation to said taps asreference potential points.

4. A measuring system as claimed in claim 1, wherein said modulatingmeans varies the frequency of said signal generator and saiddemodulating means is a frequency discriminator.

5. A measuring system as claimed in claim 1, wherein each of said coilsconsist of identical pairs of winding turns disposed in common andparallel radial planes in respect to the rotary axis of said secondmember and wherein one pair of adjoining ends of each pair of turns areconnected to one another and the remaining pairs of adjoining ends ofthe turns are connected respectively to the associated power generatorand rectifying means. g

6. A measuring system as claimed in claim 1, wherein each of saidcoupling coils consists of identical pairs of winding turns disposed incommon and parallel radial planes in respect to the axis of rotation ofsaid second member, wherein one pair of adjoining ends of each pair ofturns are connected to one another, to provide a pair of potentialreference points, wherein the remaining pairs of adjoining ends of saidturns are connected respectively to the associated power generator andrectifying means, and wherein said signal generator and receiving meansare connected respectively to said reference points.

7. A measuring system as claimed in claim 1, wherein said digital signalproducing means comprises a rack upon said first member, a pinionengaged by said rack, and an analog-digital converter to convert therotational angles of said pinion into proportionate numbers of digitalsignal pulses.

8. A measuring system as claimed in claim 7, wherein said analog-digitalconverter comprises a rotating shutter having alternate peripheralopaque and transparent segments and driven by said pinion, a stationaryshutter having opaque and transparent segments similar to and alignedwith the segments of said rotating shutter, and photo-electric pickupmeans including a light source and a number of photoelectric cellsdisposed on opposite sides of said shutters, to produce current pulsesin a circuit including said cells proportional in number to therotational angle of said pinion.

9. A measuring system as claimed in claim 7, wherein said analog-digitalconverter is designed to produce a first digital pulse series and asecond similar pulse series in quadrature relation to said first seriesand leading and lagging respectively said first series in dependenceupon the sense of rotation of said pinion, encoding means to combineboth said pulse series into a single ternary pulse series for modulationof said signal generator and having positive and negative pulsescorresponding respectively to the sense of rotation of said pinion, anddecoding means connected to said demodulating means, to reconvert thedemodulated ternary signals into the original quadrature pulse series.

1. A system of digital measurement of the position of a first memberslidably mounted upon a second rotating member comprising incombination:
 1. a first stationary coupling coil,
 2. a second similarcoupling coil upon said rotating member coaxial with the rotary axisthereof and parallel to said first coil,
 3. a stationary high-frequencypower generator connected to said first coil,
 4. means mounted on saidsecond member and including rectifying means connected to said secondcoil, to rectify the energy induced in said second coil from said firstcoil and provide a d.c. power source upon said second member,
 5. meansmounted on said second member and energized by said power source toproduce digital signals representative of the position of said firstmember relative to said second member,
 6. a high-frequency signalgenerator mounted upon said second member,
 7. means to modulate theoutput signal of said signal generator by said digital signals,
 8. meansto apply the output energy of said signal generator to said second coil,9. a stationary receiving means connected to said first coil to derivesignal energy induced in said first coil from said second coil, and 10.demodulating means connected to said receiving means, to reproduce theoriginal digital signals.
 2. A measuring system as claimed in claim 1,wherein the carrier frequency of said signal generator is different fromthe carrier frequency of said power generator.
 2. a second similarcoupling coil upon said rotating member coaxial with the rotary axisthereof and parallel to said first coil,
 3. a stationary high-frequencypower generator connected to said first coil,
 3. A measuring system asclaimed in claim 1, wherein said coils are provided with center taps andthe energy of said power generator is transmitted in symmetricallybalanced relation and the energy of said signal generator is transmittedin unbalanced relation to said taps as reference potential points.
 4. Ameasuring system as claimed in claim 1, wherein said modulating meansvaries the frequency of said signal generator and said demodulatingmeans is a frequency discriminator.
 4. means mounted on said secondmember and including rectifying means connected to said second coil, torectify the energy induced in said second coil from said first coil andprovide a d.c. power source upon said second member,
 5. A measuringsystem as claimed in claim 1, wherein each of said coils consist ofidentical pairs of winding turns disposed in common and parallel radialplanes in respect to the rotary axis of said second member and whereinone pair of adjoining ends of each pair of turns are connected to oneanother and the remaining pairs of adjoining ends of the turns areconnected respectively to the associated power generator and rectifyingmeans.
 5. means mounted on said second member and energized by saidpower source to produce digital signals representative of the positionof said first member relative to said second member,
 6. a high-frequencysignal generator mounted upon said second member,
 6. A measuring systemas claimed in claim 1, wherein each of said coupling coils consists ofidentical pairs of winding turns disposed in common and parallel radialplanes in respect to the axis of rotation of said second member, whereinone pair of adjoining ends of each pair of turns are connected to oneanother, to provide a pair of potential reference points, wherein theremaining pairs of adjoining ends of said turns are connectedrespectively to the associated power generator and rectifying means, andwherein said signal generator and receiving means are connectedrespectively to said reference points.
 7. A measuring system as claimedin claim 1, wherein said digital signal producing means comprises a rackupon said first member, a pinion engaged by said rack, and ananalog-digital converter to convert the rotational angles of said pinioninto proportionate numbers of digital signal pulses.
 7. means tomodulate the output signal of said signal generator by said digitalsignals,
 8. A measuring system as claimed in claim 7, wherein saidanalog-digital converter comprises a rotating shutter having alternateperipheral opaque and transparent segments and driven by said pinion, astationary shutter having opaque and transparent segments similar to andaligned with the segments of said rotating shutter, and photo-electricpickup means including a light source and a number of photoelectriccells disposed on opposite sides of said shutters, to produce currentpulses in a circuit including said cells proportional in number to therotational angle of said pinion.
 8. means to apply the output energy ofsaid signal generator to said second coil,
 9. a stationary receivingmeans connected to said first coil to derive signal energy induced insaid first coil from said second coil, and
 9. A measuring system asclaimed in claim 7, wherein said analog-digital converter is designed toproduce a first digital pulse series and a second similar pulse seriesin quadrature relation to said first series and leading and laggingrespectively said first series in dependence upon the sense of rotationof said pinion, encoding means to combine both said pulse series into asingle ternary pulse series for modulation of said signal generator andhaving positive and negative pulses corresponding respectively to thesense of rotation of said pinion, and decoding means connected to saiddemodulating means, to reconvert the demodulated ternary signals intothe original quadrature pulse series.
 10. demodulating means connectedto said receiving means, to reproduce the original digital signals.